Conventional compressible fluid motors include a rotor positioned within a cylindrical rotor cavity with the rotor having vanes arranged in radial slots in the rotor. These types of motors are commonly known as radial vane motors. The rotor is usually positioned eccentrically within the cavity, requiring the rotor vanes to move in and out of the rotor as it rotates. During the power portion of the rotation, the vanes are "kicked out" of their radial slots in order to expose a greater surface to the incoming pressurized fluid. As the vanes approach the end (or top) of the power stroke, the vanes contact the cylinder wall and are forced by the wall into their respective slots as the rotor rotates past the top of the stroke.
Various devices and methods are known in the art for kicking out the rotor vanes. A common method simply utilizes the incoming air pressure to urge the vanes out from the rotor. The pressurized air starts the rotor rotating, and once it is rotating it generates a centrifugal force that is sufficient to urge the vanes out of their slots. However, the air only method is slow in starting up the rotor and is unsatisfactory during periods of low pressure.
Another common method for extending the rotor vanes uses springs or spring devices that bias the vanes out toward the cylinder wall. These spring devices help to ensure good rotor start capabilities and continued operation under low air supply pressure. However, one of the problems with spring devices is the chronic fatigue failure of the spring mechanism. The spring mechanism is constantly flexing as the vanes move in and out of the rotor. The flexing continues even after the rotor is rotating fast enough to generate a centrifugal force sufficient to force the vanes out from the rotor without the assistance of the spring. This continual flexing causes fatigue failure of the spring mechanism, which can create problems in the operation of the motor. The spring may weaken or break due to the continued flexing, thereby severely limiting the start-up capabilities of the motor. Furthermore, a piece of a broken spring may lodge in the slot and prevent the radial vane from moving in and out of the slot as the rotor rotates, resulting in extended downtime for disassembly and repair of the motor. Thus, a need exists for a device that will kick-out the rotor vanes initially at start-up and under low air flow conditions and that will be deactivated when the rotor is rotating sufficiently to generate a centrifugal force to urge the vanes out from the rotor.